1. Field of the Invention
The present invention relates to a toilet tank valve structure, and more particularly to a structure to control a knob and having a limiting device for a partial discharge.
2. Description of the Prior Art
As shown in FIG. 1, a conventional toilet tank valve comprises a knob 10, a rotatable shaft 20, a pole 30, first and second pull wires 40, a whole discharge assembly 50, a partial discharge assembly 60, and a water seal 70. When the knob 10 is turned clockwise or contraclockwise, the rotatable shaft 20 will link the pole 30 to turn clockwise or contraclockwise so as to pull the first or second pull wire 40 to lift the water seal 70 at different levels, releasing a whole discharge or a partial discharge.
The above-mentioned structure has the following disadvantages:                1. The knob 10 is operated at two different directions to release a whole discharge or a partial discharge, which is easy to cause a confusion to turn the wrong direction.        2. It is necessary to provide enough space for clockwise or contraclockwise rotation of the knob 10, therefore, the installation of the knob is limited and not convenient.        3. The front of the toilet tank is provided with a toilet cover. Due to the toilet cover, the knob 10 is not suitable for installing at the front of the toilet tank. Usually, the knob 10 is installed at one side of the toilet. The knob 10 tends to hit the wall easily when the knob 10 is turned toward the wall, which is not convenient to operate the knob 10.        4. When the knob 10 is installed at one side of the toilet tank, people are used to turn the knob outward not inward, which is unable to achieve two-stage function and is easy to have a wrong operation.        5. The whole discharge or the partial discharge depends on the whole discharge assembly 50 or the partial discharge assembly 60. The knob 10 doesn't have a partial discharge limit mechanism itself, which is not easy for a user to identify the whole discharge or the partial discharge by hand.        